Prostaglandins E2, F2 alpha, D2, prostacyclin (PGI2) and thromboxane A2 as well as the 13,14-dihydro-15-keto-PGE2 and F2 alpha metabolites will be measured in culture fluids of cells derived from normal and malignant tissue and in conditioned media of normal and malignant tissues incubating in organ culture, and also in peripheral plasma of mice carrying various transplanted tumors. These arachidonic acid products reflect the following enzyme activities: 1) phospholipase A2, 2) cyclooxygenase, 3) thromboxane synthetase, 4) prostacyclin synthetase, and 5) the PG synthetase system composed of PGD2 and PGE2 isomerase and PGF2 alpha reductase. The question of whether the profiles of these enzymic activities in normal and malignant cells vary in a predictable manner or whether they are unique to each cell, normal or malignant, will be answered.